The problem arising from supporting ladders upon nonlevel support surfaces wherein the supports for the legs are not in the same horizontal plane are well known and numerous types of devices have been proposed to compensate for this condition. Such devices include adjustable extensions affixed to each ladder leg, arcuate adjustable supports and self-leveling extensions wherein frictional locking engagement of the extension with the ladder is produced by the weight of the operator upon the ladder. Such devices have not provided the answer to the problem since manually adjustable leg extensions and arcuate supports require time consuming adjustment at each location of the ladder and existing self-locking leveling devices do not lock with the desired positive action so as to prevent malfunctions and consequently do not provide the insurance of safety necessary when using a ladder. Actual experience also has shown that the attention of painters, workmen, etc. may be directed to other matters causing them to forget to lock and unlock a manually operated leveling device causing a safety hazard.
Many of these problems have been overcome by a self-leveling ladder attachment shown in U.S. Pat. No. 2,894,670 of which I am a coinventor thereof. However, it has been found that such attachment devices are relatively bulky and difficult for the average home owner to install with sufficient confidence that the leveling attachment will work in the manner intended and with the required safety. Furthermore, the self-leveling attachment of my earlier invention required a considerable number of specially designed component parts which increased the weight and cost of the attachment making it less attractive for purchase by the average home user desiring a self-leveling ladder. It is believed that the home user desires such a self-leveling ladder if it does not increase the weight of the ladder appreciably and if the leveling device is formed as a part of the ladder eliminating any attachment or addition to of the ladder after purchase. Furthermore, the reduction in the number of parts required to achieve the automatic self-leveling effect reduces both the cost and weight of the ladder which is very attractive to the home user.
Examples of known prior art self-leveling devices are shown in U.S. Pat. Nos. 2,552,941; 2,598,875; 3,027,969; 3,037,581; 3,173,512; 3,215,383; 3,233,702; 4,095,671; 4,128,139 and 4,497,390. Although the devices of some of these patents do provide a ladder having a self-leveling mechanism incorporated as a part of the ladder in contrast to a separate leveling attachment therefor, these devices require an excessive number of parts thereby increasing the complexity of the ladder, the cost and the possibility of maintenance problems. Furthermore, many of these self-leveling devices and ladders are not automatic and require manual manipulation of a locking device to secure the ladder in the adjusted level position.
Therefore, the need has existed for an improved automatic self-leveling ladder in which the self-leveling mechanism is formed as a part of the ladder and requires a minimum number of components thereby providing an inexpensive, lightweight yet highly efficient and safe ladder construction.